1. Field of the Invention
The present invention relates to a bidirectional light waveguide telecommunication system and more particularly to such a system which employs a plurality of telecommunication equipment that each comprise a combined opto-electrical receiving/electro-optic transmitting module including a laser circuit which is provided with a monitor photodiode which is used for the dual purpose of acting as a receiver and as a monitor utilized for controlling the operating point of the laser diode by way of a frequency-separating filter connected to the monitor diode which is connected to a demodulator for the received signals and a control circuit for controlling the operating point of the laser diode.
2. Description of the Prior Art
Recent developments in telecommunications technology have lead to light waveguide telecommunication systems wherein the light waveguides can be respectively utilized in both transmission directions. (In this connection, one is referred to Geisler, Beaven and Boutruche, "Optical Fibers", EPO Applied Technologies Series Vol. 5, 1986, pp. 552-586), namely in isopositional wavelength operation upon employment of, for example, direction-separating filters constructed with a partially-reflecting mirror or an (integrated optical) directional coupler (see Soejima, Yamashita and Kuwahara, Zurich Seminar '86 Conf. Paper B3, pp. B3.1-B3.8, Section 1 in Table 1), or in wavelength separation mode, i.e. in what is referred to as bidirectional wavelength multiplex (WDM-Wavelength Division Multiplex) upon utilization of appropriate wavelength filters (Zurich Seminar '86 Conf., Paper B3, pp. B3.1-B3.8, Section 3 in Table 1), in that light waves having a shorter wavelength are employed for the signal transmission via (preferably monomode) optical fibers in the one transmission direction and light waves having a longer wavelength are employed for the signal transmission in the other transmission direction. In both instances, appropriate optical separating filter modules are to be provided at the two ends of the light wave guide, these modules respectively effecting a separate light-guiding connection from the light waveguide to the respective opto-electric transducer and from the respective electro-optical transducer to the light waveguide. Direction-separating filters can also be provided in combination with a time separation mode (Zurich Seminar '86 Conf., supra, Section 4.1 in Table 1), whereas, conversely, no additional direction-separating filters need be provided given the time separation mode when the light-emitting diode or, respectively, a monitor photodiode provided for controlling the operating point thereof is also utilized as a receiving diode (Zurich, Seminar '86 Conf., supra, Section 4.3 in Table 1; German published application 38 22 803 A1, published May 3, 1989).
The introduction of new telecommunication systems having light waveguide (LWG) line trunks or central office lines is quite generally dependent on the type and scope of the telecommunication infrastructures already existing, together with the telecommunication services offered therein, and on the demand for new broadband communication services. The potentially-greatest volume of connections is thereby envisioned in the domain of private households; this potential for connections, however, will not be reflected in an effective demand for connections without correspondingly-low costs of a broadband subscriber connection.
It has already been provided (European Patent Application 89 117 968.1) in this context in a bidirectional light waveguide telecommunication system for wavelength division duplex (bidirectional WDM) between a central telecommunication location and a plurality of decentralized telecommunication locations, particularly having a passive LWG bus network extending between a switching center and a plurality of subscriber locations, that an electro-optical transmission element and an opto-electric transmission reception element that are designed for wavelength division multiplex are provided only the central telecommunication location, whereas a combined opto-electric receiving/electro-optic transmission module that is free of wavelength filters, works in the time separation mode and is designed for the emission of light having a wavelength for whose reception the central telecommunication location is equipped is respectively provided in the decentralized telecommunication locations, this combined module being formed with a laser module provided with a monitor photodiode which is utilized as a receiving diode in alternation with its monitoring function. Due to the signal running time and dependent on the burst data rate and the burst length, however, the distance that can be bridged in a time separation mode is fundamentally limited.